Hard disk drives are common information storage devices. FIG. 1a provides an illustration of a typical disk drive unit 100 essentially consisting of a series of rotatable disks 101 mounted on a spindle motor 102, and a Head Stack Assembly (HSA) 130 which is rotatable about an actuator arm axis 105 for accessing data tracks on disks during seeking. The HSA 130 includes at least one drive arm 104 and HGA 150. Typically, a spindling voice-coil motor (VCM) (not shown) is provided for controlling the motion of the drive arm 104.
Referring to FIG. 1b, the HGA 150 includes a slider 103 having a reading/writing transducer (not shown) imbedded therein, a suspension 190 to load or suspend the slider 103 thereon. When the disk drive is on, a spindle motor 102 will rotate the disk 101 at a high speed, and the slider 103 will fly above the disk 101 due to the air pressure drawn by the rotated disk 101. The slider 103 moves across the surface of the disk 101 in the radius direction under the control of the VCM. With a different track, the slider 103 can read data from or write data to the disk 101.
FIG. 1c shows a conventional suspension, the suspension 190 includes a load beam 106, a base plate 108, a hinge 107 and a flexure 105, all of which are assembled together.
The load beam 106 is connected to the base plate 108 by the hinge 107. A locating hole 112 is formed on the load beam 106 for aligning the load beam 106 with the flexure 105. And the load beam 106 is welded with the flexure for increasing the strength of the entire structure.
The base plate 108 is used to enhance structure stiffness of the whole HGA 150. A mounting hole 113 is formed on one end of the base plate 108 for mounting the whole HGA 150 to the motor arm 104 (referring to FIG. 1a). Another hole 110 is formed on the other end of the base plate 108, which is aligned with a hole 110′ formed on the hinge 107 and a hole 110″ formed on the flexure 105. The hinge 107 has a mounting hole 131′ formed on its one end corresponding to the mounting hole 113 of the base plate 108, and the hinge 107 is partially mounted to the base plate 108 with the mounting holes 131′, 113 aligned with each other. The hinge 107 and the base plate 108 may be mounted together by laser welding at pinpoints 109 distributed on the hinge 107. Two hinge steps 115 are integrally formed at two sides of the hinge 107 at one end adjacent the mounting hole 131′ for connecting with the flexure 105.
The flexure 105 runs from the hinge 107 to the load beam 106. The flexure 105 has a proximal end 119 adjacent the hinge 107 and a distal end 118 adjacent the load beam 106. A locating hole 112′ is formed on the distal end 118 of the flexure 105 and aligned with the locating hole 112 of the load beam 106, thus obtaining a high assembly precision. A suspension tongue 116 is provided at the distal end of the flexure 105 to carry the slider 103 thereon.
As illustrated in FIG. 1d, the flexure 105 has a leading portion 121 adjacent the suspension tongue 116, and a tailing portion 122 opposite to the leading portion 121. A plurality of electrical traces 120 is formed on the flexure 105 along length direction thereof. More specifically, the electrical traces 120 begin with the leading portion 121 and terminate at the tailing portion 122. The suspension tongue 116 has a plurality of bonding pads 117 formed thereon for coupling the slider 103. One end of the electrical traces 120 connects to the bonding pads 117, and the other end thereof is electrically connected to a preamplifier (not shown). Generally, the electrical traces 120 extending from the bonding pads 117 includes three pairs (but not limited to three pairs of trace) which respectively are a couple of read traces 123, write traces 124 and heat traces 125 as shown in FIG. 1e. All of traces will be jointed to several terminal pads 126 at the tailing portion 122.
FIG. 1f shows a cross-section view of the detailed structure of the flexure 105 taken along the line A-A shown in FIG. 1d. The flexure 105 has a laminate structure 130 including a resilient stainless steel layer 131 and a polyimide layer 133 formed on the stainless steel layer 131. The read traces 123, write traces 124 and heat traces 125 are formed on the polyimide layer 133. Therein, the write traces 124 includes a positive write trace 1241 and a negative write trace 1242, which will operate as a differential pair. Accordingly, it is difficult to realize simultaneously the low impedance, high bandwidth in this microstrip type trace pair because the capacitive coupling is not strong enough. Ultimately, the impedance of the electrical traces is large, and finally affecting the writing operation of the slider 103.
In view of it, an improved suspension with stacked electrical traces had been developed. U.S. Pat. No. 7,986,495B2 discloses improved electrical trace pair with one write trace formed on an upper trace layer and another write trace formed on a lower trace layer. As shown in FIG. 2a, insulating layer 40 is composed of first, second and third insulting layers 41, 42, 43. The first insulating layer 41 is formed on the suspension body 10. And the write trace W1 (negative) for writing information in a magnetic disk (not shown) and the read trace R1 for reading information from the magnetic disk are formed on the first insulating layer 41. The write trace W2 (positive) and the read trace R2 are formed on the second insulating layer 42. With this design, the impedance of the write traces is lower. Especially, the impedances of the write traces on the upper trace layer and the lower trace layer can be adjusted to the same value by adjusting the width of the write traces. Thus the improved suspension with stacked electrical traces is advanced due to its lower impedance and reduced crosstalk.
However, as the distance between the write traces on the upper trace layer and the grounding layer (that is the suspension body 10) is different from that between the write trace on the lower trace layer and the grounding layer, thus the electrical performance of the write traces on the upper trace layer and the lower trace layer are different. For example, the signal propagation time of the upper trace layer and the signal propagation time of the lower trace layer are not balanced, which may cause signal distortion, especially in high data rate transmission condition. As shown in FIG. 2b, it can be seen that, the signal propagation times in the positive write trace and the negative write trace are different.
Thus, there is a need for an improved suspension with improve stacked electrical traces, an HGA and a disk drive unit that do not suffer from the above-mentioned drawbacks.